In breeds where an elective cesarean is routine, the hardest question is not whether to operate. It is when. Go too early and you deliver puppies that were not ready. Wait too long and you risk being overtaken by labour, or by a complication in the middle of the night.
Progesterone C-section timing is the most objective approach available for that decision, and the numbers behind it are genuinely good. They are also more limited than the confident charts circulating online suggest. This article covers both halves honestly, because the second half is the part that gets left out.
Read this before the numbers
De Cramer and Nöthling, whose 2018 Theriogenology study established the thresholds below, state in that same paper that controlled studies large enough to be convincing are still required before it can be considered safe to routinely perform a cesarean section once progesterone falls below a defined threshold. Nothing on this page is a surgical decision rule. Scheduling a cesarean is a veterinary decision that weighs the dam, the litter, the breed, the history, and the clinical picture — with progesterone as one input among several.
- Progesterone 5 ng/mL or above means under a 2% chance of spontaneous whelping in the next 12 hours — useful for ruling a night out.
- Below 2.8 ng/mL, 99% whelp within 48 hours. Below 1.0 ng/mL, 100% do.
- The LH surge is the best gestational anchor at about 65 days, but prediction is only within ±1 day about 67% of the time.
- The evidence supports progesterone as an input, not as a standalone trigger for surgery.
If you run a Finecare Vet or Pro-DX
The figures above come from laboratory and reference-method literature. This analyzer reads on its own scale and sits systematically higher: independent testing puts the regression at Finecare = 5.87 + 1.28 × reference, so on the Finecare chart estimated ovulation falls at 8–15 ng/mL and the fertile range at 15–40 ng/mL. Time from the chart supplied with your kit lot, not from the numbers in this article. Why thresholds belong to the assay that produced them →
Why the calendar alone is not enough
Start with what a date can and cannot give you. De Cramer puts the gestational anchors as follows: measured from the LH surge, gestation runs about 65 days; from ovulation, about 63; from fertilization, about 61 — with the latter two explicitly less accurate than the first. Measured from the breeding date it spans roughly 58 to 68 days, which is far too wide to schedule surgery against.
Even the best anchor is a window rather than a point. Kutzler and colleagues, writing in Theriogenology in 2003, measured how precisely the date of the initial preovulatory progesterone rise predicts parturition:
That is genuinely useful for planning. It is not precise enough, on its own, to pick an operating slot. A one-in-three chance of being off by more than 24 hours is exactly the margin that catches breeders who booked travel for the calculated date.
The calendar tells you which week. Progesterone tells you which day. Neither tells you the hour on its own.
What the prepartum numbers actually say
In dogs, labour is preceded by an abrupt collapse in progesterone as the corpora lutea break down. Because that drop is large and tightly coupled to labour onset, it can be read as a countdown in a way that is not possible in most other species.
The most underrated row is the top one
Most attention goes to the low thresholds, but the 5 ng/mL line is arguably the more practical finding for a breeder. Fewer than 2% of pregnant bitches at that concentration enter spontaneous whelping within the following 12 hours, which places her at low risk of needing overnight observation.
Knowing a female is not going to whelp tonight is worth as much to an exhausted breeder in week nine as knowing that she is. It converts a fortnight of broken sleep into targeted vigilance.
Where the evidence stops
This is the section that most articles on progesterone C-section timing omit, and it matters more than any threshold.
The published probabilities describe when a bitch is likely to whelp on her own. They do not, by themselves, establish when it is safe to operate. Those are related questions, but they are not the same question, and the gap between them is exactly what the original authors flagged in the closing line of their own results.
Two practical consequences follow:
- A number is not a green light. A progesterone value below a threshold does not authorise surgery. It contributes evidence that the pregnancy has reached term and that luteolysis has begun.
- Assay differences compound the uncertainty. Thresholds in the literature were established on particular assays. Nöthling and De Cramer found chemiluminescence readings averaging only 85% of paired radioimmunoassay values on canine samples, with a 95% confidence interval spanning 58% to 112% — so a value of “1.9” on one instrument is not necessarily “1.9” on another. Serial testing on a single analyzer, showing the direction of travel, carries more information than one absolute number.
Do not manage this alone
If you are breeding a brachycephalic or otherwise high-risk breed, the planning conversation should begin weeks before the due window, not on the day a number crosses a line. Ask your veterinarian which anchor they want you to record, which analyzer they want results from, and at what point they want to be called.
How progesterone C-section timing works in practice
The workflow that gets the most out of progesterone in the final week looks roughly like this.
- Record Day 0 during the heat cycle. Everything downstream depends on it. Count 65 days from the LH surge to define the expected window.
- Agree the plan in advance. Discuss with your veterinarian when to start prepartum sampling, usually a few days before the calculated window opens.
- Sample daily as the window approaches, on one analyzer, at a consistent time of day.
- Watch the trajectory, not just the value. A fall from 12 to 6 to 3 over three days tells you more than a single reading of 3.
- Combine with the other signals your veterinarian uses: rectal temperature, behaviour, and where relevant fetal monitoring.
Step 3 is the one that fails most often, and usually for logistical rather than clinical reasons. Daily sampling in the final week is impractical if every result means a clinic trip and a wait. As De Cramer notes, turnaround time is precisely what impedes the usefulness of commercial laboratory assays in cases where an immediate clinical decision is needed — which is the situation point-of-care progesterone was built for. The PETlife Pro-DX from Wondfo USA returns a quantitative canine progesterone (cProg) result from 75 µL of whole blood, serum or plasma in about 15 minutes, with no calibration step, so a daily reading is realistic rather than aspirational. Results can be exported over Wi-Fi, and logged against the individual dog in the free Pup Planner app so the falling curve is visible to whoever is making the call.
Whatever you use, the same discipline applies as during ovulation timing: one platform for the whole series, the analyzer recorded alongside every value, and interpretation against that instrument’s own reference range rather than a chart written for a different device.
Frequently asked questions
What progesterone level is used to schedule a C-section?
There is no single agreed number, and De Cramer and Nöthling explicitly note that larger controlled studies are still needed before routine threshold-triggered surgery can be called safe. In practice, veterinarians use the fall toward and below roughly 2 ng/mL as one signal that term has been reached, alongside gestational dating and clinical assessment.
Is progesterone better than temperature monitoring?
It measures the underlying event directly rather than a downstream consequence, and it is less easily confounded by ambient conditions, activity, or inconsistent technique. Most clinicians use both rather than choosing between them.
How early should prepartum testing start?
That depends on your gestational anchor and your veterinarian’s protocol. Because Kutzler and colleagues found prediction from the initial progesterone rise correct within ±1 day only about two thirds of the time, starting a few days before the calculated date is usually sensible.
Can I use a value from a different clinic’s analyzer?
It is best avoided. Progesterone platforms disagree systematically on the same sample, so mixing instruments in a prepartum series can create an apparent fall or rise that reflects the machine rather than the dog.
Sources
De Cramer KGM, Nöthling JO. The precision of predicting the time of onset of parturition in the bitch using the level of progesterone in plasma during the preparturient period. Theriogenology. 2018;107:211–218.
Kutzler MA, Mohammed HO, Lamb SV, Meyers-Wallen VN. Accuracy of canine parturition date prediction from the initial rise in preovulatory progesterone concentration. Theriogenology. 2003;60(6):1187–1196.
Nöthling JO, De Cramer KGM. Comparison of progesterone assay by chemiluminescence or radioimmunoassay for clinical decision-making in canine reproduction.
De Cramer K. Simplifying the Canine Reproductive Cycle Using the Concentration of Progesterone. IDEXX Laboratories, CLD-12211-00.
Keep reading
This article is educational and is not a substitute for veterinary advice. It does not provide a threshold at which surgery should be performed. Cesarean section is major surgery and the decision to schedule one, and its timing, must be made by a veterinarian who has examined the animal. Threshold values cited are assay-dependent and are not interchangeable between analyzers.